Multiple molecules exist on the surface of lymphocytes which are important for the development of the immune response. A major goal of these studies is to identify and structurally characterize these membrane-bound molecules, especially those present on cytotoxic T lymphocytes. Concordantly, it is important to have an understanding of the molecules encoded by infectious agents which are recognized by the immune system. Thus, the nature of the antigens in several viruses posing serious health problems is being investigated. Project areas include: (l) studies on the primary structure of the human T cell molecules T3 and T8; (2) preparation of mouse-human T cell hybrids in order to try to obtain a stable source of human T cell molecules; (3) characterization of the molecules of antigenic importance in human T cell leukemia viruses (HTLV); and (4) studies on antigenic variation in Herpes simplex virus type 1 (HSV-1) glycoproteins.